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Infectious Agent

A microorganism that causes disease, like bacteria, viruses, or parasites.

Reservoir

A place where the infectious agent lives and multiplies (e.g., humans, animals, water).

Susceptible Host

A person who can get sick because they have no immunity.

Chain of Infection

The steps an infection goes through to spread: agent → reservoir → transmission → host.

Interruption (of chain)

Breaking the chain by killing the germ, removing the reservoir, or protecting the host.

Eradication

Completely wiping out a disease, usually by removing animal sources and using vaccines.

Zoonotic Disease

A disease that spreads from animals to humans.

Factors in New Disease Emergence

Deforestation, travel, wildlife contact, and drug use that increase disease risk.

Surveillance

Monitoring for disease outbreaks to act early.

Antibiotic Resistance

When bacteria stop responding to antibiotics, making infections harder to treat.

Bioterrorism

Using germs or biological agents to cause harm on purpose.

Health Belief Model (HBM)

A theory that explains health behavior based on personal beliefs.

Perceived Susceptibility

Belief about how likely you are to get a disease.

Perceived Severity

Belief about how serious a disease or its effects are.

Perceived Benefits

Belief that an action will reduce the risk or impact of illness.

Perceived Barriers

Belief about what’s stopping you from acting (cost, fear, etc.).

Cues to Action

Triggers that remind or encourage you to act (e.g., advice, messages).

Self-Efficacy

Belief in your ability to take action and succeed.

Transtheoretical Model (TTM)

A model describing the steps people go through to change a behavior.

Pre-contemplation

Not thinking about change yet.

Contemplation

Thinking about making a change soon.

Preparation

Getting ready to act, making a plan.

Action

Actively trying to change behavior.

Maintenance

Keeping the new behavior going over time.

Socio-Ecological Model (SEM)

A model showing that behavior is shaped by many levels of influence.

Individual Level

Your personal knowledge, attitude, or choices.

Interpersonal Level

Influence from family, friends, and close relationships.

Institutional Level

Influence from schools, workplaces, and organizations.

Community Level

The local culture, norms, and physical environment.

Policy Level

Government rules and laws that affect public health.